[PATCH] Check \0-termination of string in c_getstr (simplified version)

[Martin Liška]

Hello.

After receiving feedback from Richi and Wilco Dijkstra, I decided to fully not
support not null-terminated strings. It brings more complications and the code 
has started
to be overengineered. Thus c_getstr accepts only such strings and as a bonus it 
returns
length of a string.

Patch can bootstrap on ppc64le-redhat-linux and survives regression tests.

Ready to be installed?
Martin

>From bee44f0dedc86b1c354e21dd87dad6313147dcc3 Mon Sep 17 00:00:00 2001
From: marxin <mli...@suse.cz>
Date: Thu, 13 Oct 2016 10:20:12 +0200
Subject: [PATCH 1/4] Support only \0-terminated string in c_getstr and return
 strlen

gcc/ChangeLog:

2016-10-13  Martin Liska  <mli...@suse.cz>

	* fold-const.c (c_getstr): Support of properly \0-terminated
	string constants.  New argument is added.
	* fold-const.h: New argument is added.
---
 gcc/fold-const.c | 38 +++++++++++++++++++++++++++++---------
 gcc/fold-const.h |  2 +-
 2 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 02aa484..57a9243 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -14440,24 +14440,44 @@ fold_build_pointer_plus_hwi_loc (location_t loc, tree ptr, HOST_WIDE_INT off)
 }
 
 /* Return a char pointer for a C string if it is a string constant
-   or sum of string constant and integer constant.  */
+   or sum of string constant and integer constant.  We only support
+   string constants properly terminated with '\0' character.
+   If STRLEN is a valid pointer, length (including terminating character)
+   of returned string is stored to the argument.  */
 
 const char *
-c_getstr (tree src)
+c_getstr (tree src, unsigned HOST_WIDE_INT *strlen)
 {
   tree offset_node;
 
+  if (strlen)
+    *strlen = 0;
+
   src = string_constant (src, &offset_node);
   if (src == 0)
-    return 0;
+    return NULL;
 
-  if (offset_node == 0)
-    return TREE_STRING_POINTER (src);
-  else if (!tree_fits_uhwi_p (offset_node)
-	   || compare_tree_int (offset_node, TREE_STRING_LENGTH (src) - 1) > 0)
-    return 0;
+  unsigned HOST_WIDE_INT offset = 0;
+  if (offset_node != NULL_TREE)
+    {
+      if (!tree_fits_uhwi_p (offset_node))
+	return NULL;
+      else
+	offset = tree_to_uhwi (offset_node);
+    }
+
+  unsigned HOST_WIDE_INT string_length = TREE_STRING_LENGTH (src);
+  const char *string = TREE_STRING_POINTER (src);
+
+  /* Support only properly null-terminated strings.  */
+  if (string_length == 0
+      || string[string_length - 1] != '\0'
+      || offset > string_length)
+    return NULL;
 
-  return TREE_STRING_POINTER (src) + tree_to_uhwi (offset_node);
+  if (strlen)
+    *strlen = string_length - offset;
+  return string + offset;
 }
 
 #if CHECKING_P
diff --git a/gcc/fold-const.h b/gcc/fold-const.h
index 637e46b..bc22c88 100644
--- a/gcc/fold-const.h
+++ b/gcc/fold-const.h
@@ -182,7 +182,7 @@ extern bool expr_not_equal_to (tree t, const wide_int &);
 extern tree const_unop (enum tree_code, tree, tree);
 extern tree const_binop (enum tree_code, tree, tree, tree);
 extern bool negate_mathfn_p (combined_fn);
-extern const char *c_getstr (tree);
+extern const char *c_getstr (tree, unsigned HOST_WIDE_INT *strlen = NULL);
 
 /* Return OFF converted to a pointer offset type suitable as offset for
    POINTER_PLUS_EXPR.  Use location LOC for this conversion.  */
-- 
2.9.2